1. Field of the Invention
The present invention relates generally to a Radio Frequency (RF) front end of a Base Station (BS) in a wireless communication system. More particularly, the present invention relates to an RF front-end apparatus of a BS for optionally supporting Time Division Duplex (TDD) and Frequency Division Duplex (FDD) in a wireless communication system.
2. Description of the Related Art
Time Division Duplex (TDD) and Frequency Division Duplex (FDD) are schemes for distinguishing transmission and reception signals in a wireless communication system. In the TDD scheme, a single frequency is used for both transmission and reception but the transmission and reception are performed at different times. More specifically, the TDD scheme divides a time interval and performs transmission during a first period of the time interval and performs reception during a remaining time of the interval. In the FDD scheme, transmission and reception are performed at the same time, but the transmission and reception are performed on different frequency bands which are allocated to each of the transmission and reception signals.
FIGS. 1A and 1B are block diagrams illustrating a construction of a Base Station (BS) in a wireless communication system according to the conventional art.
FIG. 1A is a block diagram illustrating a construction of a BS employing the TDD scheme. The BS includes a baseband processor 110, an Intermediate Frequency (IF) processor 120 and a Radio Frequency (RF) processor 130. Referring to FIG. 1A, when the BS is in a transmission mode the baseband processor 110 codes, demodulates, converts an information bit stream into a baseband digital signal and provides the digital signal to the IF processor 120. The IF processor 120 converts the received baseband digital signal into an IF band analog signal and provides the analog signal to the RF processor 130. The RF processor 130 converts the IF band analog signal into an RF band signal and transmits the RF band signal through an antenna.
Construction of the RF processor 130 will now be described in detail. The RF processor 130 includes a Power Amplifier (PA) 131, a Low Noise Amplifier (LNA) 132 and a Time Division Duplexer (TDD) 134. The PA 131 amplifies a transmitted signal and the LNA 132 amplifies a received signal. The TDD 134 includes a switch 135 and a BandPass Filter (BPF) 136. The switch 135 connects the PA 131 with the BPF 136 during a transmission time and connects the LNA 132 with the BPF 136 during a reception time. The BPF 136 denies transmission of all frequency bands of an input signal except for a frequency band used for transmission and reception. Thus, the BS can perform transmission and reception at desired time intervals due to a switching operation of the switch 135.
FIG. 1B is a block diagram illustrating a construction of a BS employing the FDD scheme. In the FDD BS shown in FIG. 1B, a baseband processor 110 and an IF processor 120 are the same as those of the TDD BS shown in FIG. 1A and only a construction for duplex in an RF processor 140 is different. The RF processor 140 includes a PA 141, an LNA 142 and a Frequency Division Duplexer (FDD) 144. The PA 141 amplifies a transmitted signal and the LNA 142 amplifies a received signal. The FDD 144 includes a transmission BPF 145 and a reception BPF 146. In a transmission mode, the transmission BPF 145 denies transmission of all frequency bands of a signal input from the PA 141 except for a transmission band and transmits the result through an antenna. In a reception mode, the reception BPF 146 denies transmission of all frequency bands of a signal received through the antenna except for a reception band and provides the result to the LNA 142. In order to prevent a transmission mode signal from the PA 141 being provided to the LNA 142 and to prevent a reception mode signal from the antenna being provided to the PA 141, a circulator can also be positioned between the antenna and the BPFs 145 and 146. Thus, the BS can perform transmission and reception classified by a frequency band due to operation of the BPFs 145 and 146.
The decision of whether to employ the TDD or FDD scheme is made at the time a system is designed. Once the decision is made, a BS is configured having a fixed type according to the TDD or FDD scheme. It would be advantageous if there were a system capable of supporting both the TDD and FDD schemes. However, because the conventional TDD 134 and the FDD 144 are constructed differently from each other, as shown in FIGS. 1A and 1B, a change from one duplex scheme to another must be implemented in a manner such as adding a new type of duplexer which may include the removing of an existing duplexer.
In this case, a system manager must be able to separately manage the duplexer previously in use because the new duplexer is installed having different control parameters. Further, if a frequency band used for a communication system is different in every area in which a user desires to receive service, the degree of equipment utilization is degraded because the system manager must use a duplexer of a different band in every area in which service is to be provided. Furthermore, the degree of spectrum utilization and the chance of system utilization decrease because the system manager is limited to the system design for a diversity of frequency bands and duplex schemes.